feat: migrate ORM base to sqlmodel-ext, add file viewers and WOPI integration

- Migrate SQLModel base classes, mixins, and database management to
  external sqlmodel-ext package; remove sqlmodels/base/, sqlmodels/mixin/,
  and sqlmodels/database.py
- Add file viewer/editor system with WOPI protocol support for
  collaborative editing (OnlyOffice, Collabora)
- Add enterprise edition license verification module (ee/)
- Add Dockerfile multi-stage build with Cython compilation support
- Add new dependencies: sqlmodel-ext, cryptography, whatthepatch

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

routers/api/v1/share/__init__.py

@@ -14,7 +14,7 @@ from sqlmodels.share import (
     ShareDetailResponse, ShareOwnerInfo, ShareObjectItem,
 )
 from sqlmodels.object import Object, ObjectType
-from sqlmodels.mixin import ListResponse, TableViewRequest
+from sqlmodel_ext import ListResponse, TableViewRequest
 from utils import http_exceptions
 from utils.password.pwd import Password, PasswordStatus